Merge branch 'stable-7.0' into stable-7.1

* stable-7.0:
  ResolveMerger: Allow setting the TreeWalk AttributesNodeProvider
  Add Union merge strategy support

Change-Id: I15674134f4c73ac2de514d4fac4a36fca7ed7b07

7 files changed, 476 insertions, 4 deletions

diff --git a/org.eclipse.jgit.test/tst/org/eclipse/jgit/attributes/merge/MergeGitAttributeTest.java b/org.eclipse.jgit.test/tst/org/eclipse/jgit/attributes/merge/MergeGitAttributeTest.java
index 009ca8a152..ac30c6c526 100644
--- a/org.eclipse.jgit.test/tst/org/eclipse/jgit/attributes/merge/MergeGitAttributeTest.java
+++ b/org.eclipse.jgit.test/tst/org/eclipse/jgit/attributes/merge/MergeGitAttributeTest.java
@@ -268,6 +268,51 @@ public class MergeGitAttributeTest extends RepositoryTestCase {
 	}
 
 	@Test
+	public void mergeTextualFile_SetUnionMerge() throws NoWorkTreeException,
+			NoFilepatternException, GitAPIException, IOException {
+		try (Git git = createRepositoryBinaryConflict(g -> {
+			try {
+				writeTrashFile(".gitattributes", "*.cat merge=union");
+				writeTrashFile("main.cat", "A\n" + "B\n" + "C\n" + "D\n");
+			} catch (IOException e) {
+				throw new UncheckedIOException(e);
+			}
+		}, g -> {
+			try {
+				writeTrashFile("main.cat", "A\n" + "G\n" + "C\n" + "F\n");
+			} catch (IOException e) {
+				throw new UncheckedIOException(e);
+			}
+		}, g -> {
+			try {
+				writeTrashFile("main.cat", "A\n" + "E\n" + "C\n" + "D\n");
+			} catch (IOException e) {
+				throw new UncheckedIOException(e);
+			}
+		})) {
+			// Check that the merge attribute is set to union
+			assertAddMergeAttributeCustom(REFS_HEADS_LEFT, "main.cat", "union");
+			assertAddMergeAttributeCustom(REFS_HEADS_RIGHT, "main.cat",
+					"union");
+
+			checkoutBranch(REFS_HEADS_LEFT);
+			// Merge refs/heads/left -> refs/heads/right
+
+			MergeResult mergeResult = git.merge()
+					.include(git.getRepository().resolve(REFS_HEADS_RIGHT))
+					.call();
+			assertEquals(MergeStatus.MERGED, mergeResult.getMergeStatus());
+
+			// Check that the file is the union of both branches (no conflict
+			// marker added)
+			String result = read(writeTrashFile("res.cat",
+					"A\n" + "G\n" + "E\n" + "C\n" + "F\n"));
+			assertEquals(result, read(git.getRepository().getWorkTree().toPath()
+					.resolve("main.cat").toFile()));
+		}
+	}
+
+	@Test
 	public void mergeBinaryFile_NoAttr_Conflict() throws IllegalStateException,
 			IOException, NoHeadException, ConcurrentRefUpdateException,
 			CheckoutConflictException, InvalidMergeHeadsException,
diff --git a/org.eclipse.jgit.test/tst/org/eclipse/jgit/merge/MergeAlgorithmUnionTest.java b/org.eclipse.jgit.test/tst/org/eclipse/jgit/merge/MergeAlgorithmUnionTest.java
new file mode 100644
index 0000000000..3a8af7a00e
--- /dev/null
+++ b/org.eclipse.jgit.test/tst/org/eclipse/jgit/merge/MergeAlgorithmUnionTest.java
@@ -0,0 +1,328 @@
+/*
+ * Copyright (C) 2024 Qualcomm Innovation Center, Inc.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Distribution License v. 1.0 which is available at
+ * https://www.eclipse.org/org/documents/edl-v10.php.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+package org.eclipse.jgit.merge;
+
+import static java.nio.charset.StandardCharsets.UTF_8;
+import static org.junit.Assert.assertEquals;
+
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+
+import org.eclipse.jgit.diff.RawText;
+import org.eclipse.jgit.diff.RawTextComparator;
+import org.eclipse.jgit.lib.Constants;
+import org.junit.Assume;
+import org.junit.Test;
+import org.junit.experimental.theories.DataPoints;
+import org.junit.experimental.theories.Theories;
+import org.junit.runner.RunWith;
+
+@RunWith(Theories.class)
+public class MergeAlgorithmUnionTest {
+	MergeFormatter fmt = new MergeFormatter();
+
+	private final boolean newlineAtEnd;
+
+	@DataPoints
+	public static boolean[] newlineAtEndDataPoints = { false, true };
+
+	public MergeAlgorithmUnionTest(boolean newlineAtEnd) {
+		this.newlineAtEnd = newlineAtEnd;
+	}
+
+	/**
+	 * Check for a conflict where the second text was changed similar to the
+	 * first one, but the second texts modification covers one more line.
+	 *
+	 * @throws java.io.IOException
+	 */
+	@Test
+	public void testTwoConflictingModifications() throws IOException {
+		assertEquals(t("abZZdefghij"),
+				merge("abcdefghij", "abZdefghij", "aZZdefghij"));
+	}
+
+	/**
+	 * Test a case where we have three consecutive chunks. The first text
+	 * modifies all three chunks. The second text modifies the first and the
+	 * last chunk. This should be reported as one conflicting region.
+	 *
+	 * @throws java.io.IOException
+	 */
+	@Test
+	public void testOneAgainstTwoConflictingModifications() throws IOException {
+		assertEquals(t("aZZcZefghij"),
+				merge("abcdefghij", "aZZZefghij", "aZcZefghij"));
+	}
+
+	/**
+	 * Test a merge where only the second text contains modifications. Expect as
+	 * merge result the second text.
+	 *
+	 * @throws java.io.IOException
+	 */
+	@Test
+	public void testNoAgainstOneModification() throws IOException {
+		assertEquals(t("aZcZefghij"),
+				merge("abcdefghij", "abcdefghij", "aZcZefghij"));
+	}
+
+	/**
+	 * Both texts contain modifications but not on the same chunks. Expect a
+	 * non-conflict merge result.
+	 *
+	 * @throws java.io.IOException
+	 */
+	@Test
+	public void testTwoNonConflictingModifications() throws IOException {
+		assertEquals(t("YbZdefghij"),
+				merge("abcdefghij", "abZdefghij", "Ybcdefghij"));
+	}
+
+	/**
+	 * Merge two complicated modifications. The merge algorithm has to extend
+	 * and combine conflicting regions to get to the expected merge result.
+	 *
+	 * @throws java.io.IOException
+	 */
+	@Test
+	public void testTwoComplicatedModifications() throws IOException {
+		assertEquals(t("aZZZZfZhZjbYdYYYYiY"),
+				merge("abcdefghij", "aZZZZfZhZj", "abYdYYYYiY"));
+	}
+
+	/**
+	 * Merge two modifications with a shared delete at the end. The underlying
+	 * diff algorithm has to provide consistent edit results to get the expected
+	 * merge result.
+	 *
+	 * @throws java.io.IOException
+	 */
+	@Test
+	public void testTwoModificationsWithSharedDelete() throws IOException {
+		assertEquals(t("Cb}n}"), merge("ab}n}n}", "ab}n}", "Cb}n}"));
+	}
+
+	/**
+	 * Merge modifications with a shared insert in the middle. The underlying
+	 * diff algorithm has to provide consistent edit results to get the expected
+	 * merge result.
+	 *
+	 * @throws java.io.IOException
+	 */
+	@Test
+	public void testModificationsWithMiddleInsert() throws IOException {
+		assertEquals(t("aBcd123123uvwxPq"),
+				merge("abcd123uvwxpq", "aBcd123123uvwxPq", "abcd123123uvwxpq"));
+	}
+
+	/**
+	 * Merge modifications with a shared delete in the middle. The underlying
+	 * diff algorithm has to provide consistent edit results to get the expected
+	 * merge result.
+	 *
+	 * @throws java.io.IOException
+	 */
+	@Test
+	public void testModificationsWithMiddleDelete() throws IOException {
+		assertEquals(t("Abz}z123Q"),
+				merge("abz}z}z123q", "Abz}z123Q", "abz}z123q"));
+	}
+
+	@Test
+	public void testInsertionAfterDeletion() throws IOException {
+		assertEquals(t("abcd"), merge("abd", "ad", "abcd"));
+	}
+
+	@Test
+	public void testInsertionBeforeDeletion() throws IOException {
+		assertEquals(t("acbd"), merge("abd", "ad", "acbd"));
+	}
+
+	/**
+	 * Test a conflicting region at the very start of the text.
+	 *
+	 * @throws java.io.IOException
+	 */
+	@Test
+	public void testConflictAtStart() throws IOException {
+		assertEquals(t("ZYbcdefghij"),
+				merge("abcdefghij", "Zbcdefghij", "Ybcdefghij"));
+	}
+
+	/**
+	 * Test a conflicting region at the very end of the text.
+	 *
+	 * @throws java.io.IOException
+	 */
+	@Test
+	public void testConflictAtEnd() throws IOException {
+		assertEquals(t("abcdefghiZY"),
+				merge("abcdefghij", "abcdefghiZ", "abcdefghiY"));
+	}
+
+	/**
+	 * Check for a conflict where the second text was changed similar to the
+	 * first one, but the second texts modification covers one more line.
+	 *
+	 * @throws java.io.IOException
+	 */
+	@Test
+	public void testSameModification() throws IOException {
+		assertEquals(t("abZdefghij"),
+				merge("abcdefghij", "abZdefghij", "abZdefghij"));
+	}
+
+	/**
+	 * Check that a deleted vs. a modified line shows up as conflict (see Bug
+	 * 328551)
+	 *
+	 * @throws java.io.IOException
+	 */
+	@Test
+	public void testDeleteVsModify() throws IOException {
+		assertEquals(t("abZdefghij"),
+				merge("abcdefghij", "abdefghij", "abZdefghij"));
+	}
+
+	@Test
+	public void testInsertVsModify() throws IOException {
+		assertEquals(t("abZXY"), merge("ab", "abZ", "aXY"));
+	}
+
+	@Test
+	public void testAdjacentModifications() throws IOException {
+		assertEquals(t("aZcbYd"), merge("abcd", "aZcd", "abYd"));
+	}
+
+	@Test
+	public void testSeparateModifications() throws IOException {
+		assertEquals(t("aZcYe"), merge("abcde", "aZcde", "abcYe"));
+	}
+
+	@Test
+	public void testBlankLines() throws IOException {
+		assertEquals(t("aZc\nYe"), merge("abc\nde", "aZc\nde", "abc\nYe"));
+	}
+
+	/**
+	 * Test merging two contents which do one similar modification and one
+	 * insertion is only done by one side, in the middle. Between modification
+	 * and insertion is a block which is common between the two contents and the
+	 * common base
+	 *
+	 * @throws java.io.IOException
+	 */
+	@Test
+	public void testTwoSimilarModsAndOneInsert() throws IOException {
+		assertEquals(t("aBcDde"), merge("abcde", "aBcde", "aBcDde"));
+
+		assertEquals(t("IAAAJCAB"), merge("iACAB", "IACAB", "IAAAJCAB"));
+
+		assertEquals(t("HIAAAJCAB"), merge("HiACAB", "HIACAB", "HIAAAJCAB"));
+
+		assertEquals(t("AGADEFHIAAAJCAB"),
+				merge("AGADEFHiACAB", "AGADEFHIACAB", "AGADEFHIAAAJCAB"));
+	}
+
+	/**
+	 * Test merging two contents which do one similar modification and one
+	 * insertion is only done by one side, at the end. Between modification and
+	 * insertion is a block which is common between the two contents and the
+	 * common base
+	 *
+	 * @throws java.io.IOException
+	 */
+	@Test
+	public void testTwoSimilarModsAndOneInsertAtEnd() throws IOException {
+		Assume.assumeTrue(newlineAtEnd);
+		assertEquals(t("IAAJ"), merge("iA", "IA", "IAAJ"));
+
+		assertEquals(t("IAJ"), merge("iA", "IA", "IAJ"));
+
+		assertEquals(t("IAAAJ"), merge("iA", "IA", "IAAAJ"));
+	}
+
+	@Test
+	public void testTwoSimilarModsAndOneInsertAtEndNoNewlineAtEnd()
+			throws IOException {
+		Assume.assumeFalse(newlineAtEnd);
+		assertEquals(t("IAAAJ"), merge("iA", "IA", "IAAJ"));
+
+		assertEquals(t("IAAJ"), merge("iA", "IA", "IAJ"));
+
+		assertEquals(t("IAAAAJ"), merge("iA", "IA", "IAAAJ"));
+	}
+
+	// Test situations where (at least) one input value is the empty text
+
+	@Test
+	public void testEmptyTextModifiedAgainstDeletion() throws IOException {
+		// NOTE: git.git merge-file appends a '\n' to the end of the file even
+		// when the input files do not have a newline at the end. That appears
+		// to be a bug in git.git.
+		assertEquals(t("AB"), merge("A", "AB", ""));
+		assertEquals(t("AB"), merge("A", "", "AB"));
+	}
+
+	@Test
+	public void testEmptyTextUnmodifiedAgainstDeletion() throws IOException {
+		assertEquals(t(""), merge("AB", "AB", ""));
+
+		assertEquals(t(""), merge("AB", "", "AB"));
+	}
+
+	@Test
+	public void testEmptyTextDeletionAgainstDeletion() throws IOException {
+		assertEquals(t(""), merge("AB", "", ""));
+	}
+
+	private String merge(String commonBase, String ours, String theirs)
+			throws IOException {
+		MergeAlgorithm ma = new MergeAlgorithm();
+		ma.setContentMergeStrategy(ContentMergeStrategy.UNION);
+		MergeResult<RawText> r = ma.merge(RawTextComparator.DEFAULT,
+				T(commonBase), T(ours), T(theirs));
+		ByteArrayOutputStream bo = new ByteArrayOutputStream(50);
+		fmt.formatMerge(bo, r, "B", "O", "T", UTF_8);
+		return bo.toString(UTF_8);
+	}
+
+	public String t(String text) {
+		StringBuilder r = new StringBuilder();
+		for (int i = 0; i < text.length(); i++) {
+			char c = text.charAt(i);
+			switch (c) {
+			case '<':
+				r.append("<<<<<<< O\n");
+				break;
+			case '=':
+				r.append("=======\n");
+				break;
+			case '|':
+				r.append("||||||| B\n");
+				break;
+			case '>':
+				r.append(">>>>>>> T\n");
+				break;
+			default:
+				r.append(c);
+				if (newlineAtEnd || i < text.length() - 1)
+					r.append('\n');
+			}
+		}
+		return r.toString();
+	}
+
+	public RawText T(String text) {
+		return new RawText(Constants.encode(t(text)));
+	}
+}
diff --git a/org.eclipse.jgit/.settings/.api_filters b/org.eclipse.jgit/.settings/.api_filters
new file mode 100644
index 0000000000..f2c73f5c48
--- /dev/null
+++ b/org.eclipse.jgit/.settings/.api_filters
@@ -0,0 +1,39 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+<component id="org.eclipse.jgit" version="2">
+    <resource path="src/org/eclipse/jgit/lib/Constants.java" type="org.eclipse.jgit.lib.Constants">
+        <filter id="1142947843">
+            <message_arguments>
+                <message_argument value="6.10.1"/>
+                <message_argument value="ATTR_BUILTIN_UNION_MERGE_DRIVER"/>
+            </message_arguments>
+        </filter>
+    </resource>
+    <resource path="src/org/eclipse/jgit/merge/ContentMergeStrategy.java" type="org.eclipse.jgit.merge.ContentMergeStrategy">
+        <filter id="1176502275">
+            <message_arguments>
+                <message_argument value="6.10.1"/>
+                <message_argument value="UNION"/>
+            </message_arguments>
+        </filter>
+    </resource>
+    <resource path="src/org/eclipse/jgit/merge/ResolveMerger.java" type="org.eclipse.jgit.merge.ResolveMerger">
+        <filter id="336658481">
+            <message_arguments>
+                <message_argument value="org.eclipse.jgit.merge.ResolveMerger"/>
+                <message_argument value="attributesNodeProvider"/>
+            </message_arguments>
+        </filter>
+        <filter id="1142947843">
+            <message_arguments>
+                <message_argument value="6.10.1"/>
+                <message_argument value="attributesNodeProvider"/>
+            </message_arguments>
+        </filter>
+        <filter id="1142947843">
+            <message_arguments>
+                <message_argument value="6.10.1"/>
+                <message_argument value="setAttributesNodeProvider(AttributesNodeProvider)"/>
+            </message_arguments>
+        </filter>
+    </resource>
+</component>
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/lib/Constants.java b/org.eclipse.jgit/src/org/eclipse/jgit/lib/Constants.java
index c27047f25d..01aa925a86 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/lib/Constants.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/lib/Constants.java
@@ -547,6 +547,13 @@ public final class Constants {
 	public static final String SSH_SIGNATURE_PREFIX = "-----BEGIN SSH SIGNATURE-----"; //$NON-NLS-1$
 
 	/**
+	 * Union built-in merge driver
+	 *
+	 * @since 6.10.1
+	 */
+	public static final String ATTR_BUILTIN_UNION_MERGE_DRIVER = "union"; //$NON-NLS-1$
+
+	/**
 	 * Create a new digest function for objects.
 	 *
 	 * @return a new digest object.
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/merge/ContentMergeStrategy.java b/org.eclipse.jgit/src/org/eclipse/jgit/merge/ContentMergeStrategy.java
index 6d568643d5..a835a1dfc5 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/merge/ContentMergeStrategy.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/merge/ContentMergeStrategy.java
@@ -23,5 +23,12 @@ public enum ContentMergeStrategy {
 	OURS,
 
 	/** Resolve the conflict hunk using the theirs version. */
-	THEIRS
-}
\ No newline at end of file
+	THEIRS,
+
+	/**
+	 * Resolve the conflict hunk using a union of both ours and theirs versions.
+	 *
+	 * @since 6.10.1
+	 */
+	UNION
+}
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/merge/MergeAlgorithm.java b/org.eclipse.jgit/src/org/eclipse/jgit/merge/MergeAlgorithm.java
index 5734a25276..d0d4d367b9 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/merge/MergeAlgorithm.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/merge/MergeAlgorithm.java
@@ -120,6 +120,7 @@ public final class MergeAlgorithm {
 						result.add(1, 0, 0, ConflictState.NO_CONFLICT);
 						break;
 					case THEIRS:
+					case UNION:
 						result.add(2, 0, theirs.size(),
 								ConflictState.NO_CONFLICT);
 						break;
@@ -148,6 +149,7 @@ public final class MergeAlgorithm {
 				// we modified, they deleted
 				switch (strategy) {
 				case OURS:
+				case UNION:
 					result.add(1, 0, ours.size(), ConflictState.NO_CONFLICT);
 					break;
 				case THEIRS:
@@ -158,7 +160,7 @@ public final class MergeAlgorithm {
 					result.add(1, 0, ours.size(),
 							ConflictState.FIRST_CONFLICTING_RANGE);
 					result.add(0, 0, base.size(),
-						ConflictState.BASE_CONFLICTING_RANGE);
+							ConflictState.BASE_CONFLICTING_RANGE);
 					result.add(2, 0, 0, ConflictState.NEXT_CONFLICTING_RANGE);
 					break;
 				}
@@ -333,6 +335,15 @@ public final class MergeAlgorithm {
 								theirsEndB - commonSuffix,
 								ConflictState.NO_CONFLICT);
 						break;
+					case UNION:
+						result.add(1, oursBeginB + commonPrefix,
+								oursEndB - commonSuffix,
+								ConflictState.NO_CONFLICT);
+
+						result.add(2, theirsBeginB + commonPrefix,
+								theirsEndB - commonSuffix,
+								ConflictState.NO_CONFLICT);
+						break;
 					default:
 						result.add(1, oursBeginB + commonPrefix,
 								oursEndB - commonSuffix,
diff --git a/org.eclipse.jgit/src/org/eclipse/jgit/merge/ResolveMerger.java b/org.eclipse.jgit/src/org/eclipse/jgit/merge/ResolveMerger.java
index 50c2c1570c..033f28031a 100644
--- a/org.eclipse.jgit/src/org/eclipse/jgit/merge/ResolveMerger.java
+++ b/org.eclipse.jgit/src/org/eclipse/jgit/merge/ResolveMerger.java
@@ -41,6 +41,7 @@ import org.eclipse.jgit.annotations.NonNull;
 import org.eclipse.jgit.annotations.Nullable;
 import org.eclipse.jgit.attributes.Attribute;
 import org.eclipse.jgit.attributes.Attributes;
+import org.eclipse.jgit.attributes.AttributesNodeProvider;
 import org.eclipse.jgit.diff.DiffAlgorithm;
 import org.eclipse.jgit.diff.DiffAlgorithm.SupportedAlgorithm;
 import org.eclipse.jgit.diff.RawText;
@@ -837,6 +838,13 @@ public class ResolveMerger extends ThreeWayMerger {
 	@NonNull
 	private ContentMergeStrategy contentStrategy = ContentMergeStrategy.CONFLICT;
 
+	/**
+	 * The {@link AttributesNodeProvider} to use while merging trees.
+	 *
+	 * @since 6.10.1
+	 */
+	protected AttributesNodeProvider attributesNodeProvider;
+
 	private static MergeAlgorithm getMergeAlgorithm(Config config) {
 		SupportedAlgorithm diffAlg = config.getEnum(
 				CONFIG_DIFF_SECTION, null, CONFIG_KEY_ALGORITHM,
@@ -1502,11 +1510,23 @@ public class ResolveMerger extends ThreeWayMerger {
 				: getRawText(ours.getEntryObjectId(), attributes[T_OURS]);
 		RawText theirsText = theirs == null ? RawText.EMPTY_TEXT
 				: getRawText(theirs.getEntryObjectId(), attributes[T_THEIRS]);
-		mergeAlgorithm.setContentMergeStrategy(strategy);
+		mergeAlgorithm.setContentMergeStrategy(
+				getAttributesContentMergeStrategy(attributes[T_OURS],
+						strategy));
 		return mergeAlgorithm.merge(RawTextComparator.DEFAULT, baseText,
 				ourText, theirsText);
 	}
 
+	private ContentMergeStrategy getAttributesContentMergeStrategy(
+			Attributes attributes, ContentMergeStrategy strategy) {
+		Attribute attr = attributes.get(Constants.ATTR_MERGE);
+		if (attr != null && attr.getValue()
+				.equals(Constants.ATTR_BUILTIN_UNION_MERGE_DRIVER)) {
+			return ContentMergeStrategy.UNION;
+		}
+		return strategy;
+	}
+
 	private boolean isIndexDirty() {
 		if (inCore) {
 			return false;
@@ -1837,6 +1857,18 @@ public class ResolveMerger extends ThreeWayMerger {
 		this.workingTreeIterator = workingTreeIterator;
 	}
 
+	/**
+	 * Sets the {@link AttributesNodeProvider} to be used by this merger.
+	 *
+	 * @param attributesNodeProvider
+	 *            the attributeNodeProvider to set
+	 * @since 6.10.1
+	 */
+	public void setAttributesNodeProvider(
+			AttributesNodeProvider attributesNodeProvider) {
+		this.attributesNodeProvider = attributesNodeProvider;
+	}
+
 
 	/**
 	 * The resolve conflict way of three way merging
@@ -1881,6 +1913,9 @@ public class ResolveMerger extends ThreeWayMerger {
 					WorkTreeUpdater.createWorkTreeUpdater(db, dircache);
 			dircache = workTreeUpdater.getLockedDirCache();
 			tw = new NameConflictTreeWalk(db, reader);
+			if (attributesNodeProvider != null) {
+				tw.setAttributesNodeProvider(attributesNodeProvider);
+			}
 
 			tw.addTree(baseTree);
 			tw.setHead(tw.addTree(headTree));